Here’s one for the tech/design crowd, though with the dispersion of high-resolution displays, it will soon be relevant for everyone. Since Apple introduced the iPhone 4, there has been some debate over what qualifies as a retina display—retina quality being defined as having pixels so small the human eye cannot discern them. Richard Gaywood over at The Unofficial Apple Weblog has crunched the numbers on high-DPI (dots per inch) displays to see which devices qualify as retina displays, which come close, and which fall short.

Many people think 300 dpi is a magic number, and with some justification—the print design world often uses 300 dpi as a minimum standard. But 300 dpi is not a hard limit—when I was art director of the Berkeley Science Review (fall 2008 and spring 2009, if you’re curious), we would often cheat and use art down to 250 dpi if we had no other option. But even that’s not a good rule of thumb. To determine retina quality, DPI has to be considered along with the eye’s distance from the display. Once you take that into account, you’ll be surprised to discover what already qualifies as a retina display.